The tread of a tire is commonly provided with various features that can improve performance as well as impact the aesthetics of the tread. For example, a tread may include blocks of tread and/or ribs. The tread may be configured with apertures of various types including grooves along the lateral and circumferential directions, holes, sipes, and/or other features of various sizes and shapes. These features can improve tread wear, handling, braking, consumer appeal and other characteristics of the tire as well.
In addition to tire aesthetics, tread features can be used to improve traction such as e.g., wet and snow traction. For example, apertures of various sizes and orientations may be added to the ribs and/or blocks of a tire in varying configurations to improve the ability of the tire to grip the road surface—particularly in deleterious conditions such as rain or snow. However, apertures and other tread features can have disadvantages such as increased rolling resistance, particularly as the tire tread becomes less rigid through the addition of such features.
In a conventional approach, apertures and other tread features are added to the tire during the curing process. More specifically, first an uncured tire (i.e. a green tire) is created on a tire forming drum in a layered process where sheets of material are added in steps along with other components such as e.g., the bead cores, belts, and/or other components. A tread band is provided for a tread region. The materials are sequentially applied to a forming drum that initially provides a flat surface but ultimately moves the beads together to form the toroidal tire shape.
The resulting green tire is then placed into a curing press where heat and pressure are used to cure the tire rubber components as well as bond the rubber components together. During this curing step, the walls of the press can be equipped with intricate molding elements that impart tread features into the uncured tread of the green tire. For example, fin-like metal projections may be added to the walls of the tire press in the tread forming section in order to impart apertures such as grooves and other details to the tread as the tread is cured by pressure and heat.
The conventional manufacture of a tire with various features along the tread presents certain challenges. The nature of the molding process limits the shape and configuration of grooves and other apertures that can be added to the tire tread to apertures that can be formed by the insertion of metal projections extending from the walls of the curing press. For example, the conventional tire press can create apertures that extend from the outer surface of the tread inward, but cannot create apertures in the tire tread that appear only after a period of tread wear has occurred, i.e. hidden or covered apertures. Similarly, apertures can be created that extend radially outward from the innermost portion of the tread but conventional methods cannot create an aperture that is hidden from the bottom and top portion of the tread—i.e. conventional methods cannot create an aperture that does not extend from either the radially innermost or radially outermost surface of the tread. In addition, the manufacture of relatively thin and deep apertures using standard molding techniques is fraught with difficulties due to the fragility of mold elements needed to make such features.
Accordingly, a tire tread having apertures and a method of making such a tread would be useful. More particularly, a method that can be used to construct a tire having apertures of a certain depth that are available for enhancing traction at each of the various levels of tread wear would be particularly beneficial. Such a method that can also be used to create apertures of varying geometries, densities, and depths while still allowing for control of the rigidity of the tire tread so as to improve performance such as e.g., rolling resistance would also be useful.